The present invention relates generally to antennas and more particularly to a multi-element antenna in which each one of the elements has tapered resistive loading over its length.
For commercial and military reasons, there exists a need for an antenna that has a low standing wave ratio and has uniform radiation pattern characteristics over a wide bandwidth.
Conventional monopole and dipole antennas are two very well known and commonly used antennas. However, such antennas have many shortcomings. First, these antennas are very narrow band, thereby limiting the frequency range of operation. Second, these antennas experience large variations in their impedance characteristies when operated over large frequency bands due to multiple resonances within the antenna. Third, these antennas experience a degradation in the radiation pattern characteristics over large frequency bands. The degradation manifests itself as multiple lobes and nulls in the radiation pattern characteristics. Fourth, these antennas require complex matching circuits to obtain an instantaneous broadband system.
Broader band characteristics have been obtained with conventional monopoles and dipoles by increasing the diameter to length ratio; however, the bandwidth has still been limited.
The concept of using tapered resistive loading to improve the bandwidth of conventional monopoles and dipoles is well known in the art. Articles describing this concept include Cylindrical Antenna with Nonreflecting -Resistive Loading, IEEE Transactions On Antennas And Propagation, Vol. AP-13, No. 3, pp. 369-373, May 1965, T. T. Wu and R. W. P. King. It should be understood that the Wu-King approach is merely illustrative of one approach that may be used to make a loading profile. Other pertinent articles include Optimized Tapered Resistivity Profiles For Wideband HF Monopole Antenna, presented at the 1991 IEEE Antenna And Propagation Society International Symposium, London, Ontario Canada, pp. 1-4, B. Rama Rao; Wideband HF Monopole Antennas With Tapered Resistivity Loading, presented at MILCOM '90, 1990 IEEE Military Communications Conference, Monterey, Calif., Sep. 30-Oct. 3, 1990, pp. 1223-1227, B. Rama Rao and P. S. Debroux; The Time-Domain Characteristics Of A Traveling-Wave Linear Antenna With Linear And Non-Linear Parallel Load, IEEE Transactions On Antennas And Propagation, Vol. AP-28, No 2, March 1980, pp. 267-276, M. Kanda; and A Relatively Short Cylindrical Broadband Antenna With Tapered Resistive Loading for Picosecond Pulse Measurements, IEEE Transactions On Antennas And Propagation, Vol. AP 26, No. 3, May 1978, pp. 439-447, M. Kanda.
Articles pertaining to other types of resistively loaded antennas include, The Butterfly: A Broadband Aerodynamic Antenna For Airborne Missile Scoring Using Impulse Radar, IEEE APS Symposium Proceedings 1991, pp. 715-718 E. N. Clouston. A resistive loaded antenna having a butterfly configuration is disclosed. In an article Optimization Of A Resistively Loaded Conical Antenna For Pulse Radiation, IEEE APS Symposium Proceedings, July 1992, pp. 1968-1972, J. G. Maloney and G. S. Smith there is described a solid cone shaped antenna which is partially metallic and resistively loaded over the remainder of its surface.
In U.S. Pat. No. 5,173,713 to F. Yues et al there is disclosed a three element inverted conical monopole antenna in which each element includes a series inductance and resistance. In U.S. Pat. No. 4,302,760 to S. Laufer there is disclosed a wideband vertical doublet antenna.
It is an object of this invention to provide a new and improved antenna.
It is another object of this invention to provide an antenna that operates over a wide bandwidth.
It is still another object of this invention to provide an antenna that has a low standing wave ratio.
It is yet another object of this invention to provide an antenna that has constant radiation characteristics over a wide bandwidth.
It is a further object of this invention to provide an antenna that is lightweight.